To kiss the breasts of a woman; likewise the less honorable parts of a person of diverse sex. To kiss parts that are indeed honorable but less customarily kissed of a person of the other sex will more often be grave (cf. St. Alphonsus III, 417).
To kiss a person of diverse sex on the cheek for a long time or very often; or on the mouth with notable delay or often; or with the tongue put into the mouth of another, that is, columbine kisses, with delay or several times. This last, done once or another time and without delay, will rather often be mortal (cf. St. Alphonsus, loc. cit.).
To kiss while the lower parts of the body are pressed against the body of another.
General note. Honorable kisses, embraces, and touches between persons of diverse sex:
If done as a sign of friendship, are without fault (St. Alphonsus III, 417). "Decorum, however, must be observed here; for in many regions it is not becoming for ecclesiastical men, especially religious, to testify friendship toward women with a kiss, even if they were joined by blood."1
If done from levity, are venially evil (St. Alphonsus III, 418).
If done from sensible carnal pleasure, are venial (St. Alphonsus, loc. cit.); when they become mortal, see n. 64.